Hours into discussing his new collection with Target, Joseph Altuzarra still looked fresh-faced and cheerful. “I have stamina,” said the 31-year-old fashion designer, dressed comfortably in a gray henley, jeans and sneakers.

“I think what Target allows and gives us the opportunity to do is really invite a much broader audience into our world, and get to know our brand,” he said.

Altuzarra spoke with Speakeasy about social media, and why he chose model Eva Herzigova for the collaboration’s marketing campaign. The designer’s Target collection, priced from $18 to $90, will be available Sept. 14 at select Target stores and Target.com, with some items also available on Net-A-Porter.

Edited excerpts:

When I hear about these types of fashion collaborations, I typically think it’s designed for teenage girls or very young people. Was it a conscious decision to cast Eva Herzigova, an older model, for your campaign?Completely. From the very beginning, Target and I were very much aligned on the idea that it was not going to be this sort of girly, flirty, young collaboration. That it was going to be really for a woman. It was going to be sophisticated. There was going to be a certain seductiveness and sensuality.

These high-low collaborations have been around for a while now. Alexander Wang is partnering with H&M later this year. How do you distinguish yourself in this environment?A lot of it was really giving it a personal touch, with my being super involved in every step of the way–probably too involved. [laughs]

I think the differentiator when you’re looking at collaborations between which ones are good and which ones are not as successful is usually like, you can tell which ones are genuine and authentic and where the designer was really there, and which ones are just a label that was tacked onto a piece of product.

I think from top to bottom in our case, there was really a strategy. There was an idea. We were talking to a woman and not a girl. We were really thinking about this idea of seductiveness. This idea of intimacy–of sort of the transformative power of clothing.

From the way that we announced the partnership, which was a very thoughtful–almost counterintuitively not social-media driven announcement. We sent out personalized boxes with elements of the collection and personalized gifts to journalists and editors.

Joseph Altuzarra for Target

You mentioned taking a different approach with social media. How does that work in this day and age when tweeting and promoting yourself online are so important?Social media is of course incredibly important and I think we have to take it into account, and strategy of communication for the brand. But on the other hand I think you also have to know how to use it, and I think it’s a powerful message when you don’t use it as well, when you choose to instead do something that’s tangible and physical.

And I think the people who received those boxes, in our case, felt very special. And they felt like it was a very intimate thing, and I wrote a personal note to all of them, sort of announcing the collaboration. I think that set the tone for the rest of the collection for people to know that it was a very personal thing.

Joseph Altuzarra for Target

What considerations did you have to take into account in designing for a broader audience?In a weird way, the process and development was actually pretty similar to our own collection. As a brand, Altuzarra, we’re talking to real women as well. Whether you’re buying a $3,000 dress or a $60 dress, I actually think you’re expecting something that’s going to work for your lifestyle. You’re expecting something that’s going to fit, and something that’s going to move with your body.

What’s next for you? You’ve already hinted to us about a handbag collection.We’re very much in this incredibly expansive era in the development of the brand, and so we are working on a wide variety of products, of which accessories is one.

About Speakeasy

Speakeasy is a blog covering media, entertainment, celebrity and the arts. The publication is produced by Barbara Chai and Jonathan Welsh with contributions from the Wall Street Journal staff and others. Write to us at speakeasy@wsj.com or follow us on Twitter at @WSJSpeakeasy or individually @barbarachai.